We claim:
1. A method for improving the quality of imaging in video imaging systems,
the method comprising:
scaling the video image zone from black to white within a predefined bit range as herein described, characterized in that the scaling is performed without having to allocate a part of the digital bit range to the pedestal signal from the sync tip.
2. The method as claimed in claim 1, wherein the signal level Is IV sync tip to white peak with 25% reserved for sync tip to pedestal level.
3. The method as claimed in claim 1, wherein the method is implementable in video imaging systems having positive white peak as well as negative white peak with an appropriate change in the digital to analog level map.
4. A method of processing echo data (230) available in a video ram (280) of an imaging system (240) before being presented to a digital to analog converter (DAC) (290) for generating composite video baseband signal (330), characterized in that the method comprising:
storing said echodata in 256 levels in a local buffer (270).
generating video ram address (390) corresponding to the echo data samples positions (360) on a scanline (350)
writing buffer data (400) in the respective video ram address ;
incrementing X address of video ram (410) for IH line progressively and increment Y address of video ram after every horizontal line during video display scan time ;
reading video data (420) from corresponding video ram locations ,and presenting said data to the digital to analog converter in the right time slots, wherein the method enables achieving a resolution of 2.9mv at the DAC output (300) by feeding all 256 levels of signals in the form of echo data (230) received from the video ram (280) to the DAC (290) and scaling said signals (300) over 0 to 0.75V range.

5. An ultrasound System having an improved image resolution comprising:
analog to digital converter (ADC) (250) for receiving echo data (230)
characterized in that the echo data (230) is converted on a digital scale of 256 levels on an 8-bit analog to digital converter (ADC) (250);
a microcontroller with local buffer (270) for receiving and storing the echo data (230) from analog to digital converter (ADC) (250) and placing the echo data (230) in a video ram (280) in the right addresses; and
a digital to analog converter (DAC) (290) for receiving the echo data (230) from the microcontroller with local buffer (270), wherein a resolution of 2.9mv at the DAC output (300) is achieved by feeding all 256 levels of signals in the form of echo data (230) received from the video ram (280) to the digital to analog converter (DAC) (290) and scaling said signals (300) over 0 to 0.75V range.
6. The method as claimed in claim I to 4, wherein said method is
implementable in systems including digital televisions, set top boxes, DVDs, VCDs, TV
Cards in Personal Computers with composite video baseband signal out terminals and
digital video cameras, ASICs, FPGAs, any other programmable device implementing
MPEG decoders; encoders or combinations thereof, video encoders and all categories of
ICs wherein video encoding is carried out as one of the IC processes.

METHOD FOR IMPROVING IMAGE RESOLUTION IN VIDEO IMAGING SYSTEMS AND IMPLEMENTATIONS THEREOF
Field of the Invention
[1] In general, this invention relates to imaging systems employing composite video baseband (CVBS) signals being converted as such from digital video data by Digital to Analog Converters (DAC). More particularly, the present invention relates to a method for improving image resolution in video imaging systems and implementations thereof.
Background of the Invention
[2] There has been a constant effort for achieving higher image resolution in systems employing composite video baseband (CVBS) signals. This eventually lead to graduating from 6 bit systems through 8 bit to 10 bit systems. Typically, the composite video baseband signal (CVBS), given to a display monitor, is of lv p-p amplitude with 25 % of the amplitude reserved for accommodating the pedestal level of the CVBS signal above the tip of sync part of the signal.
[3] A Digital to Analog Converter (DAC) is used for generating the CVBS signal which has to provide IV p-p output representing the sync tip (0V) through pedestal black level (0.25V) to peak white (IV). Since the available range of IV of DAC output has to accommodate all the levels of CVBS right form sync tip at 0V to peak white at IV, a good part of the dynamic range of the DAC i.e. 0 to 0.25 V is used only for pedestal signal amplitude just above the sync tip. This corresponds to 0 to 63 digital levels at DAC input. This leaves only levels from 64 to 255 available for representing the full range of received signals.
[4] The current state of the art, therefore, scales the incoming levels of signal within 192 discrete levels between 64 and 255. This represents on the video amplitude scale of 0.75V, a resolution of 0.75/192 =3.9 mv over the CVBS amplitude of IV p-p.
[5] If incoming signals are spread in 256 levels and are accommodated within 192 levels available for representation at a resolution of 3.9mv, then every incoming signal at 256 discrete levels does not find a unique level for being presented at the DAC input. More levels of incoming signals get resolved to the same DAC input level since only 192 discrete levels only are available to accommodate 256 levels, causing inferior quality in the imaging.
[6] The present invention seeks to address the aforesaid deficiency in the known art. In doing so, and for purposes of specific illustration, the method of the present invention is explained against the background of ultrasound imaging. This is no way intended to limit the application of the disclosed method to a large arena of imaging activities employing video imaging systems.
Example of one Prior Art Embodiment - Ultrasound Imaging
[7] Ultrasound waves are sound waves beyond the audible range. Ultrasound waves used for medical imaging typically lie in 3 to 10 Mhz range. Piezo ceramic transducers are used both for transmitting and receiving ultrasonic waves. These transducers pump ultrasonic waves when excited electrically and convert reflected ultrasonic waves into electrical pulses. The reflected signals received at the transducer are suitably compressed to accommodate the high dynamic range of the signals and are made available to the input of a digital to analog converter.
[8] The ultrasonic waves are transmitted into the body by the transducer through a coupling medium like ultrasonic gel which helps in optimum transfer of ultrasonic energy into the body. Wherever the ultrasonic waves face a non-uniform interface along the depth of penetration, these waves are reflected. The ultrasonic waves suffer attenuation as they travel deep. By relating the intensity of the reflected waves received with the depth, which again depends on the time elapsed since the transmission commenced, we can construct an image of the cross section of the body along the depth plane.
[9] The key to the imaging process is the differences in impedance along the various tissues in the plane of the depth of penetration. Reflection takes place whenever there is a change in the tissue structure and hence the tissue impedance. By properly factoring loss of energy due to attenuation suffered on account of increasing depth, the variations in the intensity of reflected waves will give us the information crucial to imaging. These intensity levels are sought to be resolved into 256 gray levels on a Black and white monitor. Since gray scale differences are crucial to delineating the fine tissue differences, the gray scale which was initially at 64 levels has gone upto 256 levels.
If incoming signals are spread in 256 levels and are accommodated within 192 levels available for representation at a resolution of 3.9mv, then every incoming signal at 256 discrete levels does not find a unique level for being presented at the DAC input. More levels of incoming signals get resolved to the same DAC input level since only 192 discrete levels only are available to accommodate 256 levels, causing inferior quality in the imaging.
[11] One of the embodiments of the present invention is the implementation of the disclosed method to improve the quality of the images in ultrasound imaging.
Summary of the Invention
[12] It is the principal aspect of the present invention to devise a method for scaling the video image zone from black to white (within the defined bit range for this luminance region) without having to allocate a part of the digital bit range to the pedestal signal from the sync tip.
[13] It is an aspect of the invention to devise a method for scaling the video image zone from black to white in video imaging systems employing wherein the signal level is IV sync tip to white peak with 25% reserved for sync tip to pedestal level.
[14] It is yet another aspect of the present invention to devise a method for scaling the video image zone from black to white in video imaging systems having positive white peak as well as negative white peak with an appropriate change in the digital to analog level map.
[15] In one preferred embodiment, the present invention provides for an ultrasound transducer having an improved image resolution wherein by feeding all 256 levels of signals (in the form of echo data received from the video ram) to a digital to analog converter (DAC) and scaling said signals over 0 to 0.75V range, thus achieving a resolution of 2.9mv at the DAC output.
[16] In another preferred embodiment, the present invention provides for an ultrasound transducer having an improved image resolution of 0.75/256=2.9mv at the DAC output.
[17] It is also an aspect of the present invention to devise a method of processing the echo data available in the video ram of an Ultrasound transducer before being presented to the Digital to Analog Converter for generating composite video baseband signal wherein said echodata in 256v levels is first stored in a local buffer, generate video ram address corresponding to the echo data samples positions on a scanline, write buffo- data in the respective video ram address, increment X address of video ram for 1H line progressively and increment Y address of video ram after every horizontal line during video display scan time, read video data from corresponding video ram locations, and present said data to Digital to Analog Converter in the right time slots.
[18] In yet another aspect, the present invention provides for an ultrasound transducer having improved fidelity.
[19] In still another preferred embodiment, the present invention discloses implementing the method for scaling the video image zone from black to white (within the defined bit range for this luminance region) without having to allocate a part of the digital bit range to the pedestal signal from the sync tip thus enabling superior quality imaging in systems employing composite video baseband signals and are connected to any display medium.
In still another preferred embodiment, the present invention discloses implementing the method for scaling the video image zone from black to white (within the defined bit range for this luminance region) without having to allocate a part of the digital bit range to the pedestal signal from the sync tip thus enabling superior quality imaging in systems wherein Y signals and C signals are generated as part of s-type video format.
[21] In still another preferred embodiment, the present invention discloses implementing the method for scaling the video image zone from black to white (within the defined bit range for this luminance region) without having to allocate a part of the digital bit range to the pedestal signal from the sync tip thus enabling superior quality imaging in systems including digital televisions, set top boxes, DVDs, VCDs, TV Cards in Personal Computers with composite video baseband signal out terminals and digital video cameras.
[22] In still another preferred embodiment, the present invention discloses implementing the method for scaling the video image zone from black to white (within the defined bit range for this luminance region) without having to allocate a part of the digital bit range to the pedestal signal from the sync tip thus enabling superior quality imaging in systems including ICs, ASICs, FPGAs or any other programmable device implementing MPEG decoders; encoders or combinations thereof, and video encoders.
[23] In still another preferred embodiment, the present invention discloses implementing the method for scaling the video image zone from black to white (within the defined bit range for this luminance region) without having to allocate a part of the digital bit range to the pedestal signal from the sync tip thus enabling superior quality imaging in all types of ICs wherein video encoding is carried out as one of the IC processes.
Brief Description of the Drawing Figures
[24] Fig. 1 (prior art) illustrates a video amplitude scale of 0.75V, a resolution of 0.75/192=3.9mv over the composite video baseband amplitude of 1 Vp-p.
[25] Fig. 2 (prior art) is a system block diagram illustrating an ultrasound System implementing the method disclosed in the present invention.
[26] Fig. 3 is a schematic diagram illustrating the method of processing the echo data received from the video ram in a video imaging system.
[27] Fig. 4 illustrates the elements set selection of the probe, the scan line defined for the selected element set, the angle of the scan line with respect to the probe surface etc.
[28] Fig. 5 is a flow chart illustrating the method of processing the echo data received from the video ram employing a micro-controller and as implemented in a video imaging system.
[29] Fig. 6 illustrates a resolution of0.75/256=2.9mv at DAC output.
Fig. 7 is a diagram illustrating pedestal signal being created independently as sync signal of composite video baseband signal with amplitude varying from 0 to 0.25V.
[31] Fig. 8 is a diagram illustrating pedestal signal and video signal being generated on a common timeline.
[32] Fig. 9 illustrates one of the events in the timeline wherein illustrated is the equivalent source resistance by the non-inverting input of the IC2.
[33] Fig. 10 illustrates the timings of the various components of the CVBS signal. Detailed Description of the Preferred Embodiments
[34] While this invention has been described in detail with reference to certain preferred embodiments, it should be appreciated that the present invention is not limited to those precise embodiments. Rather, in view of the present disclosure, which describes the current best mode for practicing the invention, many modifications and variations would present themselves to those skilled in the art without departing from the scope and spirit of this invention.
[35] The method of the current invention is illustrated with the help of Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 and Fig. 8.
[36] An ultrasound transducer wherein the method of the present invention is implemented is shown in Fig. 2 wherein the array of elements in the Ultrasound transducer will be excited through high voltage for pumping ultrasound waves. Selective grouping of array elements and applying a differential delay profile to the selected elements establishes the focus. Routing of the delayed excitation signals takes place through the high voltage switching unit to the selected elements of the array. Integrated in the switching unit is also the front end receiving circuit as the same transducer is also used to receive the echos.
[37] Referring to Fig. 2, the transmitter block (100) under the contrpl of CPU/Central control (110) receives user settings of depth, focus, probe type etc and thereby establishes the delay profile applicable to the selected group of elements. The set of selected array elements at high voltage switching unit transfer the echo signals (120) to the receiver block (130). To achieve the desired receive focus, the signals (120) coming at the different elements of a selected group are combined with a differential delay profile and then made available as echo signal (pre-process) (140). The wide dynamic range of input signal (140) is compressed in the receiver (130) through a logarithmic amplifier (170) after passing through a band pass filter
(150) and variable gain amplifier(160). The variable gain amplifier (160) performs time gain compensation (TGC)(200) as per settings made by the user (220). Echo signal (230), thus processed are also affected by the signal contrast settings (190) and signal brightness settings (180) made by the user (220) and available as control signals (210) in the receiver (130).
[38] Referring to Fig. 3, the received signals (echo) (230) are presented to an Analog to Digital Converter (ADC) (250) present in the CPU unit (240) for conversion to a digital scale of 256 levels on an 8-bit ADC (250). These ADC signals (260) (corresponding to processed echo signals) spread over 256 levels are received in local buffers (270) in the CPU system (240).
[39] Referring to fig.4, the selected array element set (340), which is excited, also defines a scan line (350) direction for display of samples (360) at a specific angle to the transducer face (370). As echo signals (230)(in fig2) received are from such a scan line (350)(in fig4), the samples (360Xin fig4) are placed in video ram (280Xin fig. 3) in the right addresses. The placing of echo data (260Xin fig3) in correct video ram addresses facilitates the process of correct video display when a TV CVBS generating signal scans odd and even fields in succession as per CVBS standards through the video ram (280)(in fig3) and convert these digital data into analogue data through a DAC (290)(in fig3) i.e. signals are picked from the video ram (280) (in fig3) corresponding to their positions. The above described process is performed by the microcontroller (270) (in fig3) employing the process as illustrated in Fig. 5.
Referring to fig.3, the echo data (260) accumulated in the buffers are transferred to the video ram (280) in a process called scan conversion. The process of video ram reading is synchronised with the specifications of CVBS signal in that they are made to appear as analogue signal levels of CVBS signal during the active video period (i.e. other than the sync, front porch and back porch period.) This is facilitated by presenting the video ram signals (280) in right time slot to DAC (290) whose output generates the complete CVBS signal. CVBS generation is a process running in the CPU system (240) which integrates the different components like sync (310), pedestal level, active video signal level (300) according to their relative timings in the overall organisation of the standard CVBS as per the process illustrated in Fig. 3 and Fig. 5.
[41] In order to generate the entire 0 to IV level of CVBS (sync tip to peak white) through DAC (290) as in existing systems, the process flow running in CPU system (240) will be as illustrated in Table 1. As only 192 of 256 permissible levels of DAC are allocated to the signal range, Column 4 entries in table 1(c) represent the actual value (fractional part included) of the echo data on a 192 scale. As these are to be rounded off to the nearest integer for realization, Column 3 (b) entries represent the nearest available integers which can be presented to the DAC (290).
[42] A 'Lookup Table' as per Table 1 with Column 4 entries representing echo data
valnp anH Pnliimn ^ valnp rpmrpspntina values that can he fed tn DAC f29ft^ correspondingly has to be created in the CPU (240). There will be more than one real value getting resolved to the same value on presentation to the DAC (290). Thus by feeding all incoming 256 levels of received signals (echo data taken from video ram) to DAC (290) and scaling them over 0 to 0.75V range, a resolution of 0.75/256 = 2.9mv at DAC output can be realised Please refer to Fig.6. In order to achieve this, the entries of echo data in Column 2 of Table 1(a) spread over 256 levels are directly fed to the DAC (290) without accessing any 'Lookup Table'.
[43] By separately generating sync and pedestal signals between 0 to 0.25V and adding this sync with DAC output (300)(fig3), the desired CVBS range of IV p-p can be achieved. This leads to a better resolution of 2.9mv as against 3.9 mv as in state of the art, as illustrated in Fig.6. In fig. 3, the pedestal signal (310) is generated independently as sync signal (310) of composite video baseband signal with amplitude varying from 0 to 0.25 V. The signal indicated in Fig. 3 as pedestal signal has two levels i.e 0V during sync period and 0.25V during the rest of the composite video baseband signal (CVBS). Please refer to Fig. 10 for the timing of this signal.
[44] Referring to Fig. 8, the signal indicated therein as video signal (300) is made available as output from the DAC (290)(in fig3) during the active video period i.e. after the back porch (430) and before the front porch (440). On a common time line (450), the pedestal signal (310) and video signal (300) will be generated as illustrated in Fig.8. In Fig. 3, IC1 is used as a unity gain buffer (320) and so the output of IC1 (320) will be the same as pedestal signal (310).
[45] The events on the timeline can be further analyzed in 3 phases as illustrated in Fig. 8.
Referring to fig3,
(1) The non inverting input of IC2 (V+o) will see a voltage as follows by Thevinin's theorem.
(2) V+iC2=Video*(R4/(R4+R3))+IClo/p*(R3/(R3+R4)) [video, IClo/p, refer to voltage levels at these nodes]. The equivalent source resistance seen by the non inverting input of IC2 will be: Req = (R3 * R4)/(R3 +R4).
(3) The o/p of IC2 will be: Vic2o/P=V+ic2 *(1+(R2/R1))
[46] The application of these relationships to the 3 phases leads to the following wherein:
Phase 1 refers to the sync period when pedestal signal is at 0V and video signal is also at 0V. During this phase, IC1 o/p = 0V as IC1 is only a buffer. Applying equation 1 and 3 above it is clear that Vic2o/p = 0V during this period.
Phase 2 refers to the front porch and back porch periods when pedestal signal is at 0.25V and video signal is still 0V. Applying equation 1 above, and for given values of R3 and R4 (i.e. IK each), V+iC2 = 0 * (1/(2)) + 0.25* (1/(2)) = 0.125V. Applying equation 3, (Rl= R2=lk) Vrc2o^= 0.125 * (1 + (1/1)) = 0.25V.
Phase 3 refers to the active video period when the video voltage can go from 0 to 0.75 V max and pedestal signal is 0.25 V.
[47] Considering two cases wherein: Case 1: Video voltage = 0V
Applying equation 1 above, and for given values of R3 and R4 (i.e. IK each), V+ic2 = 0 * (1/(2)) + 0.25* (1/(2)) = 0.125V.
Applying equation 3, (Rl= R2=lk) V,C2o/p = 0.125 * (1 + (1/1)) = 0.25V
Case 2: Video voltage = 0.75V
Applying equation 1 above, and for given values of R3 and R4 (i.e. IK each), V+ic2 = 0.75 * (1/(2)) + 0.25* (1/(2)) = 0.5V.
Applying equation 3, (Rl= R2=lk) Vic2o/p = 0.5 *(1+(1/1)) = 1V
[48] By putting together events in Phases 1, 2 and 3 (2 cases), the indicated waveform for CVBS signal as desired can be achieved.
The method of improving image resolution in video imaging systems as disclosed herein can be implemented in an ultrasound transducer which will in turn lead to improve fidelity marginally. Referring to Table (Table-1), assuming well calibrated monitor and all other conditions being the same in an experiment evaluating the difference between existing and the methods herein disclosed a figure of merit for the fidelity improvement can be shown as per Table-1.
[50] In ultrasound transducers, as the reflected ultrasonic signals are used to image the cross section of scanned parts of the body, the better resolution envisaged in the present method will lead to relative gray values of the interfaces of body tissues coming out more accurately providing finer tissue differentiation. This will give greater image clarity and better feel of the anatomy of the scanned parts of the body.
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241 181 180.5137255
242 181 181.2627451
243 182 182.0117647
244 183 182.7607843
245 184 183.5098039
246 184 184.2588235
247 185 185.0078431
248 186 185.7568627
249 187 186.5058824
250 187 187.254902
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[51] Referring to Table-1, Column 2 of the table indicates echo data actual value as available in video ram and read by the process that presents data to DAC (150Xfig3). Column 3 represents data as rounded off to the nearest available integer on 192 scale from the actual value with fractional part included, shown in column 4. i.e. Entries in column 4 represent only scaling by a factor of 192/256 of entries in column 2 and except for scaling, no loss of information is there between column 4 entries and column 2 entries. This has to be distinguished from column 3 entries which are a distorted and rounded off level and therefore loss of information is present between entries in column 2 and column 3. Due to rounding off requirement many entries are found in column 3 as having same value which correspond to 2 values in column 4. Therefore difference between values i.e c(n) -c(n-l) does not show up due to merger of these distinct values into the same resolved value. When this difference is expressed as a fraction of c(n), how much distinction is lost due to rounding off can be estimated. Figure of merit is assigned to this fraction, as the same difference between two successive high levels does not show up as much as it shows up between successive lower levels.
[52] Referring to Table-1, a typical case of level 5 and level 6 on 256 scale in column2 above, if considered, both these values are resolved to level 4 in column 3 on 192 scale. On applying the figure of merit criteria as aforesaid, it can be found that about 20% difference in gray scale is brought about for a level of 6 and 5/256 in the proposed method as against the absence of this difference in existing method. The effect of fidelity upto 1% difference is carried forward as per the fourth column in the above table for a level of 98/256 and thereafter the differential effect becomes insignificant. Since it is all the more important in ultrasonic image to bring out tissue differences at low brightness intensities of deeper depth of penetration, the proposed method should add to the quality of image perception and facilitate more accurate delineation and measurements in ultrasound scanner image process.
[53] While the level of signal under discussion above has been identified as IV sync tip to white peak with 25% reserved for sync tip to pedestal level, the invention equally applies to similar systems in which there can be a variation in the absolute sync tip to peak white level and sync tip to pedestal level. The principle brought out by the invention applies to positive white peak as well negative white peak systems with an appropriate change in the Digital to analogue level map.
[54] Considering a 10 bit system in which the digital range goes from 0 to 1023(i.e 0000000000 to 1111111111). This entire range in one case can be made available as per this invention to represent only black to white luminance. On applying the principle of this invention, it is not necessary in this case to reserve any part of this range (eg.25% from 0000000000 to 0011111111) for sync tip to pedestal level and thereafter having to compress luminance within 0100000000 to 1111111111).
[55] While this invention has been described in detail with reference to certain preferred embodiments, more specifically the implementation of the methods disclosed herein in an ultrasound transducer, it should be appreciated that the present invention is not limited to those precise embodiments. The invention can be applied to the large class of video imaging systems, ICs like MPEC video encoders wherein a composite video baseband signal to PAL/NTSC format are used. In some high resolution video systems in which the digital data width is other than 8 bit as applied to the DAC like 10 bit or lower resolution systems in which the bit width is less than 8 bits also, the invention is applicable. All types of appliances/ equipment in which a composite video base band signal (CVBS) in PAL/NTSC or other formats are brought out for connection to any display medium including TV. All types of appliances/ equipment in which Y and C signals are brought out as part of s-video format. Digital TV sets, Set top Boxes, DVDs, VCDS,TV cards in PCs with CVBS out terminals, Digital movie cameras etc. ICs/ ASICs/FPGA/Other programmable devices implementing MPEG decoders, encoders their combinations, Video encoders etc. Effectively all ICs in which video encoding takes place as one of the IC processes.